I have a GM HEI that is spec'd to give a finish vacuume advance of 18* (and it does ported). It also spec's the mechanical advance to acheive 22* of advance @ 4200 rpm's (and it does). Would it be better (from performance and efficiency stand point)to allow ported vacuume to acheive the 18* and set initial timing to 4* ADC (total 36*), Or, scrap vacuume advance alltogether and adjust initial timing to 14* BTC and allow mechancial to complete 36* total. Which raises the question. Should I reduce the amount of mechanical advance and adjust the initial timing to say 20* BDC and recurve the mechanical advance to only allowan additional 16* of advance at lower RPM'S???? Any advice in how to recurve the mechanical and /or vacuume advance would be greatly appreciated.
69 camaro, warmed over 350, com[p cam (mild but noticable) w/ s/r 67cc heads 2.02 exh 1.6 int valves, Demon 650 DP, victor JR intake , Hooker headers, 1.5 Roller rockers.
thx joe c

The vacuum advance does nothing at WOT. Set the timing like it doesn't exist. You might use some lighter springs 4200 is a little high for a performance motor.

get a crane vacuum advacne kit and folow the instruction's. it come's with spring's to recurve the mechanical and a lock out plate for the vacuum advance. the vacuum can is also adjustable.

[This message has been edited by ilbl8 (edited 05-14-2001).]

have it PROFFESSIONALY done. it doesn't cost alot and usually they know more about it than we do. make sure they ask what you have for a combination,if they don't they don't know what they're doing. everything has to be considered,cam,heads,compression,intake,
headers,auto,ect.ect.ect........

Dont figure the vac advance into your total timing! With vac advance, it isnt uncommon for an engine to run at 50-60 degrees at highway cruise speeds.

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375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova

For a 350 you should be able to get full mechanical advance in under 3000 rpm. You can get a recurve kit, but also get some timing tape for your balancer if it's not degreed already. Use the recurve kit, but always veryify that the actual curve is what you want. I have yet to see any recurve kit do what they say it will.

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www.grapeaperacing.com (http://www.grapeaperacing.com)

Most small blocks like 22-24 degrees mechanical advance all in between 3200-3500 rpm on the street. Set initial around 10-12. That is a good starting point